A three-component Ginzburg-Landau theory for a triplet pairing is developed to understand the observed multiple phases in a new superconductor UTe$_2$ under pressure. Near the critical pressure $P_{rm cr}$=0.2GPa where all components are perfectly degenerate the three successive superconducting transitions are predicted to occur. The $p$-wave pairing symmetry realized in UTe$_2$ is characterized by non-unitarity and chirality with point nodes, thus time reversal symmetry spontaneously broken.
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